Given a 2D array, print it in reverse spiral form. We have already discussed Print a given matrix in spiral form. This article discusses how to do the reverse printing. See the following examples.
Input: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Output: 10 11 7 6 5 9 13 14 15 16 12 8 4 3 2 1 Input: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Output: 11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1
C++
// This is a modified code of #include <iostream> #define R 3 #define C 6 using namespace std;
// Function that print matrix in reverse spiral form. void ReversespiralPrint( int m, int n, int a[R][C])
{ // Large array to initialize it
// with elements of matrix
long int b[100];
/* k - starting row index
l - starting column index*/
int i, k = 0, l = 0;
// Counter for single dimension array
//in which elements will be stored
int z = 0;
// Total elements in matrix
int size = m*n;
while (k < m && l < n)
{
// Variable to store value of matrix.
int val;
/* Print the first row from the remaining rows */
for (i = l; i < n; ++i)
{
// printf("%d ", a[k][i]);
val = a[k][i];
b[z] = val;
++z;
}
k++;
/* Print the last column from the remaining columns */
for (i = k; i < m; ++i)
{
// printf("%d ", a[i][n-1]);
val = a[i][n-1];
b[z] = val;
++z;
}
n--;
/* Print the last row from the remaining rows */
if ( k < m)
{
for (i = n-1; i >= l; --i)
{
// printf("%d ", a[m-1][i]);
val = a[m-1][i];
b[z] = val;
++z;
}
m--;
}
/* Print the first column from the remaining columns */
if (l < n)
{
for (i = m-1; i >= k; --i)
{
// printf("%d ", a[i][l]);
val = a[i][l];
b[z] = val;
++z;
}
l++;
}
}
for ( int i=size-1 ; i>=0 ; --i)
{
cout<<b[i]<< " " ;
}
} /* Driver program to test above functions */ int main()
{ int a[R][C] = { {1, 2, 3, 4, 5, 6},
{7, 8, 9, 10, 11, 12},
{13, 14, 15, 16, 17, 18}};
ReversespiralPrint(R, C, a);
return 0;
} |
Output:
11 10 9 8 7 13 14 15 16 17 18 12 6 5 4 3 2 1
Time complexity: O(m*n) where m is number of rows and n is number of columns of a given matrix
Auxiliary Space: O(100)
Please refer complete article on Print a given matrix in reverse spiral form for more details!